1. Field of the Invention
This invention relates to crystal growth of compound semiconductors, and more particularly to crystal growth of group II-VI compound semiconductors utilizing zinc as a solvent.
Group II-VI compound semiconductors such as ZnS and ZnSe have utility in light emitting devices, such as blue light emitting diodes.
2. Description of the Related Art
The present inventors have been developing crystal growth of group II-VI compound semiconductors.
FIG. 2 illustrates an example of a liquid phase crystal growth apparatus for growing a compound semiconductor crystal, according to the inventors' prior work.
A heat sink 11 of good thermal conduction, for example formed of a quartz solid rod, is secured at the bottom of a crystal growth vessel 10 formed of a quartz tube of an appropriate inner diameter, such as 8 to 12 mm.phi.. A substrate crystal 12, which is a growth underlie, is disposed on the heat sink 11 and pressed thereon by a substrate positioner 13. The substrate positioner 13 is formed of quartz or carbon and shaped in a cylinder of an appropriate length. Zinc (Zn) solvent 14, which is first in powder form of granular shape, is contained in the vessel 10. A source crystal 15, such as a ZnSe polycrystalline disk, is disposed on the substrate positioner 13. A weight 16 formed of a solid rod, of e.g. quartz, for securing the source crystal 15 is placed on the source crystal. The vessel 10 of the crystal growth apparatus of such construction is evacuated to a vacuum of 1.times.10.sup.-6 Torr or less and sealed.
The crystal growth apparatus as described above is disposed in a temperature gradient as shown at the righthand part of FIG. 2, to dissolve the source crystal 15 located at a higher temperature portion into the solvent 14 to the saturation concentration, to let the dissolved solute be transported by diffusion, and to cause epitaxial crystal growth on the substrate 12 located at a lower temperature portion.
When a group II-VI compound semiconductor crystal, for example ZnSe, is grown by the above-mentioned growth method, the composition of the ZnSe crystal grown on the substrate becomes Zn-rich due to the use of Zn solvent, which is the group II constituent element of the grown crystal, to cause a deviation from the stoichiometric composition.